border-1px($color)
  position: relative
  &:after
    display block
    position: absolute
    left: 0
    bottom: 0
    width: 100%
    border-top:1px solid $color
    content: ' '

border-none()
  &:after
    display none

bg-image($url)
  background-image: url($url+"@2x.png")
  background-repeat no-repeat
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
    background-image: url($url+"@3x.png")
    background-repeat no-repeat
